The main reason for doing this, I think, is so that Amazon can bundle apps from various developers. By taking over the " price management " amazon can determine the combined price without upsetting the individual developers (they will be getting their minimum anyway).
Amazon's datamining will then go on and determine the ideal software "bundle's", everybody will be buying at Amazon because they get free-apps with some bundles. They will rule the WORLD, my friends. The W.O.R.L.D.